The invention is directed to a novel monohydrate of 5-(2-(4-(1,2-benzisothiazol-3-yl)-1-piperazinyl)ethyl)-6-chloro-1,3-dihydr o-2H-indol-2-one hydrochloride, a pharmaceutical composition containing said monohydrate and a method of administering said monohydrate to treat neuroleptic diseases.
U.S. Pat. No. 4,831,031 which is incorporated herein by reference, discloses 5-(2-(4-(1,2-benzisothiazol-3-yl)-piperazinyl)ethyl)-6-chloro-1, 3-dihydro-2H-indol-2-one hydrochloride of the formula ##STR1## wherein Ar is benzisothiazol-3-yl, in the hemihydrate form (hereafter "the hemihydrate"), having neuroleptic activity.